On the ordeal of quinolone preparation via cyclisation of aryl-enamines; Synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate

Pedro Horta, Marta S.C. Henriques, Elisa M. Brás, Fernanda Murtinheira, Fátima Nogueira, Paul M. O'Neill, José A. Paixaõ, Rui Fausto, Maria L.S. Cristiano

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Recent studies directed to the design of compounds targeting the bc1 protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc1 inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol-1, are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.

Original languageEnglish
Pages (from-to)765-780
Number of pages16
JournalPure and Applied Chemistry
Volume89
Issue number6
DOIs
Publication statusPublished - 27 Jun 2017

Fingerprint

Cyclization
Quinolones
Esters
Enzymes
quinoline
Lead
Spectroscopy
Crystalline materials
Proteins
Hydroxyquinolines
4-Quinolones
Quinolines

Keywords

  • Antimalarial activity
  • ICPOC-23
  • Quinoline 4-ethers
  • Quinoline-type P. falciparum bc1 complex inhibitors
  • Quinolone-hydroxyquinoline tautomerism
  • Structural studies
  • Synthesis of quinolones

Cite this

Horta, Pedro ; Henriques, Marta S.C. ; Brás, Elisa M. ; Murtinheira, Fernanda ; Nogueira, Fátima ; O'Neill, Paul M. ; Paixaõ, José A. ; Fausto, Rui ; Cristiano, Maria L.S. / On the ordeal of quinolone preparation via cyclisation of aryl-enamines; Synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate. In: Pure and Applied Chemistry. 2017 ; Vol. 89, No. 6. pp. 765-780.
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abstract = "Recent studies directed to the design of compounds targeting the bc1 protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc1 inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol-1, are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.",
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On the ordeal of quinolone preparation via cyclisation of aryl-enamines; Synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate. / Horta, Pedro; Henriques, Marta S.C.; Brás, Elisa M.; Murtinheira, Fernanda; Nogueira, Fátima; O'Neill, Paul M.; Paixaõ, José A.; Fausto, Rui; Cristiano, Maria L.S.

In: Pure and Applied Chemistry, Vol. 89, No. 6, 27.06.2017, p. 765-780.

Research output: Contribution to journalArticle

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T1 - On the ordeal of quinolone preparation via cyclisation of aryl-enamines; Synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate

AU - Horta, Pedro

AU - Henriques, Marta S.C.

AU - Brás, Elisa M.

AU - Murtinheira, Fernanda

AU - Nogueira, Fátima

AU - O'Neill, Paul M.

AU - Paixaõ, José A.

AU - Fausto, Rui

AU - Cristiano, Maria L.S.

PY - 2017/6/27

Y1 - 2017/6/27

N2 - Recent studies directed to the design of compounds targeting the bc1 protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc1 inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol-1, are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.

AB - Recent studies directed to the design of compounds targeting the bc1 protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc1 inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol-1, are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.

KW - Antimalarial activity

KW - ICPOC-23

KW - Quinoline 4-ethers

KW - Quinoline-type P. falciparum bc1 complex inhibitors

KW - Quinolone-hydroxyquinoline tautomerism

KW - Structural studies

KW - Synthesis of quinolones

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M3 - Article

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SP - 765

EP - 780

JO - Pure and Applied Chemistry

JF - Pure and Applied Chemistry

SN - 0033-4545

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